In a conventional automotive air conditioning system, as disclosed in Japanese Patent Publication No. 2001-301438, a heating operation is performed by a heat exchanger for heating (heater core), which is provided in a hot water circuit of an automotive engine and uses engine cooling water (hot water) as a heating source. In this system, a cooling operation is performed by an evaporator (corresponding to a heat exchanger for cooling in the above publication) in a refrigerating cycle, in which a compressor device, a condenser device, a depressurizing device, and an evaporator are connected in a closed circuit.
However, it takes a certain time until the heating operation brings out its heating effect, because the heater core brings out its heating function only after a temperature of the engine cooling water has increased above a predetermined temperature after a start of the engine. For vehicle users, it is strongly desirable that the heating operation is achieved immediately after they get into the vehicle, especially in a cold season such as winter.